Yamaha DT 125 DERESTRICTING

[Lukas55]

@SpookDog Thanks for advance dude!

[Lukas55]

Does my DT sound properly?
https://youtu.be/Id1jsvah8T8

[SpookDog]

I sounds like a dog!
Seriously though, it sounds a bit ‘clicky’ to my ear. A bit hesitant as well maybe...
It’s really hard to tell without being there and hearing the whole range of sound frequencies...

P.S. Have you done your power valve yet?...

[declan]

@Lukas55 hate to say it but that engine sounds screwed i trust that yeis hole is blocked on the inlet manifold right?

[Calum]

Yeah where is your YEIS bottle?

[SpookDog]

Any old 2litre bottle top will plug the hole...
I didn’t want to say before but does that piston look like it was partially heat seized? Those are vertical score marks, no?
Not that I haven’t run a lot worse before 🤪
Sort out the power valve and see how it runs after bud. Then worry about if the top ends rattling. It could even be too much back pressure from an over closed power valve making the piston slap??

P.S. is that the side bottle, or the one that sits on top of the inlet manifold?...
My eyes aren’t as good as they once were...

[Lukas55]

@SpookDog It changed sound when I tried to adjust power valve... Maybe I should try to put it in position it was before.
Where is yeis bottle supposed to be?

[declan]

@Lukas55 IF YOUR cylinder has been rebored but your pv hasn't been machined the piston will hit your pv check the piston with the exhaust off again

[Calum]

@declan has to be a few rebores. You are okay on just one rebore.

If the valve is pinned open it will sound loud. Also if the rubber gaskets are knackered on the powervalve end caps it will sound gash.

[declan]

@Calum sure but it is a dt not exactly new bikes who knows how many bores it’s been through

[Calum]

@declan Should say on the piston

[SpookDog]

It’s over 57mm I think that it needs reprofiling ...

Make sure the power valve isn’t 180 degrees out. As long as it is fully open when the engine is off it’s ok. That and the cables are right. You should notice a huge increase in performance. Let us know how you get on...

[DTR+NSR]

Best way of checking the valve is open when it should be, is to rev the bike over 7k. Then turn the ignition off (while it's above 7k). Then check the position of the valve. From what I've heard on here, different years operate the cleaning cycle etc of the valve differently.
If it's revving out fine in fifth. It might just be down to a not 100% healthy engine not having the power to pull 6th gear well.

[Lukas55]

So when it is closed (when the bike is off) it looks like this...
https://www.youtube.com/watch?v=kephUMfdNIo&ab_channel=oupzy

So the sound comes on higher RPMs when the valve is open I guess... Can I adjust it with cables on the side of the cylinder so there is less chance of hitting the piston or it is only possible with the cylinder off?
BTW sorry for my bad English...

[Lukas55]

@DTR-NSR you mean that I remove exhaust after doing that and check it in the exhaust port or am I supposed to check it on the side of the cylinder?

[DTR+NSR]

@Lukas55 removing the exhaust is the best way to check it 100%. You could always mark the power valve pulley and housing, with some paint or similar, while you have the exhaust off and the valves in the fully open position. That'll save you having to keep removing the exhaust to check. Just make sure you turn the engine off with the key switch once it's revved above 7k rpm.

[Lukas55]

@DTR-NSR Is it smart to do that with the exhaust of?

[SpookDog]

It is not supposed to be closed down like that. It is supposed to be as open as it can be. It only closes (less than that as well!!) when it does a cleaning cycle when you turn the key, and when the engine is running at low revs...

You can see the pulley move clockwise to close the valve when it cycles ant then when you run the engine at lower revs ...

Again OPEN when the engine is not running...

[SpookDog]

You need to remove the pulley/cables from the end of the power valve, then rotate it anti-clockwise about a third of a turn (until you can see as much piston as possible) then replace the pulley/cables.
Check the the pulley moves clockwise, then back, when you turn the ignition key. If it moves anti-clockwise you have the cables back to front...
Please do this...

[DTR+NSR]

@SpookDog I think it's the angle of the pics that's making the valve look more closed than it is. As if you look at the edge of the powervalve nearest the exhaust it looks close to level with the surface of the exhaust port.